ANTS AND ANT LIFE. 87 



their nest when rain threatened ; about fifty of them were 

 always required for pushing this backwards and forwards (?) 

 If this observation be correct, it proves that the ants under 

 certain circumstances know how to perform the task of 

 closing and opening their door in suitable fashion. 



The doors are often guarded by special sentries, which 

 fulfil their important duty in various ways. Forel saw a 

 nest of the Colobopsis truncata, the two or three very small 

 round openings of which were watched by soldiers, arranged 

 so that their thick cylindrical heads stopped them up, just 

 as a coi-k stops up the mouth of a bottle. The same ob- 

 server saw the Myrmecina Latreillei defend themselves 

 against the invasions of the slave-making Strongylognathus, 

 by placing a worker at each of the little openings of the 

 nest, which quite stops up the opening either with its head 

 or abdomen. The Camponotus species also defend their nests 

 by stretching their heads in front of the openings, drawing 

 back the antennae. Each approaching enemy thus receives 

 a sharp blow or bite delivered with the whole weight of the 

 body. McCook noticed in the nests of the soon to be 

 described Pennsylvanian mound-building ants, the employ- 

 ment of special sentries, which lay watching within the nest 

 entrances, and sprang out at the first sight of danger to 

 attack the enemy ; and it was wonderful to see with what 

 swiftness the news of such an alarm spread through the 

 nest, and how the inhabitants came out en masse to meet the 

 enemy. The Lasius species defend their large, strong, and 

 very extensive nests against hostile attack or sieges with 

 equal courage and skill, while other timid species seek to 

 fly as speedily as possible with their larvae, pupae, and 

 fruitful queens. There is, as Forel tells us, a regular barri- 

 cade fight. Passage after passage is stopped and defended 

 to the uttermost, so that the assailants can only advance step 

 by step. Unless the latter are in an enormous majority, the 

 struggle may last a very long time with these tactics. During 

 this time, other workers are busy preparing subterranean 

 passages backwards for eventual flight. Generally such 

 passages are already made, and during a fight a new dome 

 of the Lasius may be seen rising at a distance, it not being 

 difficult for them to make this with the help of their extended 

 subterranean passages and communications. 



In addition to these enforced changes of dwelling, there 



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